This project examines the organization, structure and function of the TCA cycle by metabolic engineering and high-resolution 13C NMR. This past year, the oxidation of [3-13C]propionate to glutamate via the TCA cycle was measured in wild-type (WT) and citrate synthase (CS) mutant E. coli transformed with chimeric CS-MDH or CS-HSA. The 13C NMR spectra indicated that the anaplerotic flux was substantial. The CS-MDH chimeras had a greater relative oxidative flux compared to the CS-HSA transformant. These observations support the conclusion that a complex of TCA cycle enzymes, CS-MDH, channels substrates and selectively enables the entry of substrates via the CS reaction by the oxidative pathway.